A common practice in the computer software industry is to update binary code by way of a patch. Application of a patch to existing binary code results in updated binary code. In its simplest form, a patch is a set of commands for creating the updated binary code using the existing binary code. For example, the patch may include a set of copy and insert commands. A copy command includes a reference to a section of the existing binary code that matches a section of the updated binary code. The copy command is useful when a portion of the updated binary code can be obtained from the existing binary code. An insert command provides data to be inserted in the updated binary code. The insert command is used to create portions of the updated binary code that cannot be found in the existing binary code.
In practice, the “copy” command in a patch rarely involves copying an exact portion of the existing binary code for inclusion in the updated binary code. Usually, the “copied” portion of the existing binary code is similar, but not exactly the same, as the desired portion of updated binary code. Accordingly, the patch may also include an associated difference file. The copy command is used to indicate that a portion of the updated binary code is similar to the existing binary code, and the associated difference file contains the byte-wise differences. Each copy command may specify an offset in the existing binary code and a length. The specified portion of the existing binary code is read and added to the same number of bytes from the associated difference file to create the desired portion of the updated binary code.
The conventional method of patching a binary image is to create a backup of the old image, generate a new image by applying the patch to the old image, and then overwrite the old image with the newly generated image once it has been completed. This approach requires a substantial amount of free memory space, which may not be available In memory-scarce environments, such as mobile electronic devices.
One option for conserving memory space is to apply the patch incrementally to the existing binary image in memory, overwriting portions of the image as the patch executes. This option can produce viable patches but the incremental overwriting of the old portions of the image can result in a patch that must inject (rather than copy) substantial portions of the new image. Because the patch is implemented incrementally, the old image is incrementally overwritten, meaning that old sections of the image are not available for copying into the new image. The reduced amount of data available for copying may result in a larger patch.
Accordingly, it would be advantageous to provide a method and system for generating an incremental patch that improves the amount of reuse of data that will be available during the patching process. It would also be advantageous to provide a method and device for incrementally patching a binary image.
Similar reference numerals may have been used in different figures to denote similar components.